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The BIG Racquet: Remembering Howard Head and His Prince Tennis Racquet Patent

by Arthur H. Seidel

Summer 2003, Vol. 66, No. 2

As I pass my fifty-fifth year in practice in intellectual property law, I am prone to look back on memorable people and inventions I have known. One of the most interesting in both categories was Howard Head and his Prince tennis racquet, now the world’s largest-selling tennis racquet configuration.

In the early 1970s I received an unexpected telephone call from Head. Although I have never skied in my life, my daughter is an avid skier. For this reason, Head’s name was known to me as the inventor of both the Head metal skis and plastic skis, which had made a revolutionary change in ski construction by replacing the age-old wooden skis.

Head’s voice in our initial conversation, as in all my later discussions with him, was cheerful and gung ho. One quickly got the impression that he deemed nothing was impossible for him to accomplish. Head said he had been told that I was a “creative” patent lawyer, and he wanted this type of lawyer to help him patent his new large head tennis racquet invention, which he had been told was unpatentable.

I asked him to describe his invention. He said he had determined that all standard-sized tennis racquets, then having a strung surface of approximately seventy square inches, were relatively inefficient when compared to his larger racquet. He had applied physics principles to both the standard racquets and to his new racquet, treating both as complex levers for which he had developed approximate equations. Both his theoretical and experimental work convinced him that the standard-sized racquets were vastly inferior to his larger racquet. He said he had gone further and was exploring optimal parameters for his larger racquet. In discussing his new tennis racquet with his former patent counsel, however, he had been told that increasing the size of a device did not constitute anything more than an unpatentable mechanical change.

I told him that this was the normal rule. Notwithstanding this, I also told him that if it could be shown that the change in size produced a disproportionate or unexpected result, then the change in size might be patentable. The law distinguished the latter change as being a patentable change in kind, rather than an unpatentable change in degree.

A few days later, Head came to my office. This was to be the first of many meetings extending over several years and spaced at monthly intervals during which we worked out what was needed to patent his racquet.

Howard Head was a memorable man in many ways. He was a lean six feet, four inches, broad shouldered and muscular, with a shaved head and a wisp of a trimmed mustache. He resembled a young Howard Hughes, whom I had seen in newsreels shortly after the war.

We hit it off from our first meeting onward. I learned that a few years before, when in his late fifties, he had sold his Head Ski Company and retired to an estate outside Baltimore. He had built several tennis courts on his estate, wishing to learn the game, which he had never played. Within a short time after being instructed in tennis he decided that the then-universal tennis racquet was a very poor implement indeed. Accordingly, he had vowed to replace it. He was convinced that he could do this because after graduating from Harvard in the mid-1930s, with majors in physics and English, he had spent many years as an aircraft body designer in Baltimore for the Glenn L. Martin Company. This design work had made him an expert in two technical areas relevant to his new tennis racquet design, namely, the control of stresses on irregularly shaped levers and also experience with low-weight materials having high tensile strengths.

At our first meeting I had emphasized the importance of quantitative numerical data to support a valid patent on his oversized racquet. In particular, I stressed that anecdotal evidence would be of little value. Our typical discussion probed how to numerically quantify Head’s improvements.

Head bought Prince Manufacturing, Inc. in Princeton, New Jersey, so that he could obtain its technology and develop an apparatus suitable for his tennis racquet research as well as continuing to sell tennis ball throwing equipment and gain insight in tennis equipment. His research on improving the Prince tennis ball throwing machine had led to the development of the best tennis ball throwing machine then available. Within a few years, his tennis ball machines accounted for more than fifty percent of the United States total market for tennis ball throwing machines. Thus, when his tennis racquet research required a tennis ball throwing machine that could consistently deliver a tennis ball to a preselected area at a known velocity, Head had spared no effort nor expense to successfully accomplish this.

While Thomas Edison had said that inventing was ten percent inspiration and ninety percent perspiration, I found that with Head it was ten percent inspiration and ninety percent exasperation. Anything short of perfection in a mechanical device upset him. He was and could be somewhat tolerant of the human feelings and imperfections of others, but poor mechanical design infuriated him. This approach was combined with complete confidence that he could solve any mechanical problem and a disbelief in past approaches by others.Shortly after taking up the sport of tennis in his “retirement,” Head had determined that conventional tennis racquets did not perform as most tennis players intuitively believed.

Specifically, in a conventional tennis racquet, the center of percussion—popularly known as its “sweet spot,” where an impacting ball results in a zero kick or jar to the player’s hand—was close to the racquet’s throat and not, as widely believed, in the center of the racquet’s strung surface where the average player tended to strike or sought to strike the ball in play. Under the laws of physics, the center of percussion is the point on the racquet’s surface where almost the entire energy of the stroke goes into the return of the ball and none is wasted on the transmission of jar to the player’s hand.

Sophisticated tennis racquet manufacturers had recognized this discrepancy. They had attempted to shift the center of percussion toward the tip of the racquet head by putting weights on the racquet’s far tip. These attempts did not prove satisfactory; they altered the balance of such racquets to an objectionable “head heavy” feel.

Before commencing his research, Head had determined that the U.S. Lawn Tennis Association had no requirements for tennis racquets other than the avoidance of “spaghetti stringing.” Spaghetti stringing is the use of multiple strings in place of the single string universally used in all tennis racquets. Spaghetti stringing resulted in spins on the ball in all directions that cannot be reasonably controlled by the user. This loss of control virtually reduces almost all players to a common denominator. Since there was no prohibition in using any shape in a tennis racquet, even a broom, Head had a clean slate on which to practice his ideas.

While the tests conducted by Head established the superiority of his Prince racquet—and thus allowed him to acquire a utility patent on it—he concluded that for the racquet to be a commercial success, a wide spectrum of tennis players would have to be comfortable with it. For this reason, Head felt that he had to determine and use the parameters of a conventional tennis racquet in his Prince.

Head had numerous racquets prepared that were separately numbered in different classifications. These racquets were then distributed to tennis players from country clubs in the Baltimore and Washington, D.C., areas. In addition to being numbered, each racquet’s physical properties, length, weight, strung surface dimensions and center of gravity location was recorded. Head went to great lengths to try to approximate a distribution conforming to the tennis-playing population. He obtained the best estimates of players in different skills categories so that his racquet would be tested by a bona fide sampling of the population.

Head understood statistical sampling methods for quality control purposes from his industrial experience. He applied this knowledge to develop appropriate groupings in terms of player skills and preferences. He determined that large numbers of players readily detected a racquet weight change of as little as one-half ounce. Also, changing the overall length of a racquet from its normal range of lengths of twenty-six to twenty-eight inches was deemed unacceptable by a high proportion of players. Hence, he did not do it.

Over the many months that Head was involved in his racquet research, I gained increased insight into both tennis racquets and Head. He always refused to accept defeat despite the nature of the obstacle. While in Chicago during the Housewares Show, one of the largest trade shows in the world, we had to stay overnight unexpectedly to complete a negotiation. The Chicago papers had reported that there were no decent hotel rooms anywhere within the city. This did not upset Head in the least. We went to the hotel desk of one of the best hotels in Chicago, where Head put a fifty dollar bill in front of the desk clerk and stated: “I bet you fifty dollars that you don’t have rooms for this gentleman and for me for the night.” The clerk seemed mesmerized by the fifty dollar bill and finally muttered “you lose,” pocketed the money and gave us two rooms. My conscience bothered me for weeks, thinking of the two hotel guests who probably arrived late that night and were told there were no rooms available.

Every U.S. utility patent—which covers the structure and function of an article or machine, while a design patent covers only the ornamentation of an article—has at its end one or more claims that define the scope of the alleged invention. Claim One of Head’s Patent 3,999,756 is the broadest of Head’s claims and sets forth the metes and bounds of his invention:
“A tennis racket comprising a frame having a head connected to a handle grip so as to have an overall length of 26 to 28 inches and a weight of 12 to 15 ounces, said head having a strung surface of 85 to 130 square inches, the length of said surface in a direction along the longitudinal axis of the racket being between 12 and 15 inches and between 45 and 58% of the total length of the racket, said surface having a maximum width between 91/2 and 111/2 inches in a direction generally perpendicular to said axis, the center of percussion of said surface being approximately adjacent the geometric center thereof, and the center of gravity of the racket being at a location between 45 and 52% of the total length of the racket as measured from the butt end of the handle grip.”

Within the parameters of Claim One, more specific claims specified the optimal racquet length of twenty-seven inches, the generally elliptical head, the inclusion of a zone having a coefficient of restitution greater than 0.6 and a racquet length of twenty-six to twenty-seven inches.

Further intensive research by Head revealed that a higher coefficient of restitution and improved angle of return were not the only improved results from the Prince design. The dwell time of the ball on the stringed portion of the racquet was longer with the Prince. This enabled a player less skilled in the art of “follow through” to return a more controlled volley and to achieve more ball spin.

In addition, the Prince racquet proved to be far stronger and more durable than conventional racquets. This likely occurred because of less vibration and fatigue being introduced into the racquet’s frame. The reduced vibration and fatigue also minimized the jar to the player’s arm when the ball is struck at a point remote from the center of percussion, and it lessened the player’s ailment known as “tennis elbow,” an inflammation in the elbow joint caused by twisting the racquet when a ball is struck off center.

Head decided that he could not rapidly achieve distribution everywhere. Hence, he would license competitors under his patent provided they made quality racquets. Within a few years, Head’s patented construction was the largest-selling racquet configuration throughout the world. Head sold Prince Manufacturing in the early 1980s for about thirty times more than his total investment in it. This did not include the substantial profits that were made during each prior year of the company’s existence.

Of far greater importance to Head than the tens of millions of dollars he made from the sale of his company was the knowledge that he had revolutionized two disparate sports, skiing and tennis, the latter of which he had never played until his mid-fifties.

Fast forward to 2003. Howard Head has been dead for more than ten years. His patent on the Prince racquet has been expired for almost a decade. My boutique firm merged into Drinker Biddle & Reath LLP in 2001 to provide its patent section, where I am of counsel.

I had just left a sporting goods store with my granddaughter, the youngest of my five grandchildren, after buying her first tennis racquet. Naturally, it was a Prince. She asked me: “Grandpa, did you notice that my racquet was bigger than many of the others in the store?”

“Yes, I did notice that.”

Testing the Design
To prove the patentability of his new designs, Howard Head used a finely calibrated Prince tennis ball throwing machine. A tennis ball covered with chalk dust, so that its impact point could be accurately determined, was propelled at a fixed distance of five feet at speeds ranging from thirty to sixty miles per hour against the head of a racquet fixedly held in a vise, simulating a player’s hand. Head then searched for, and ultimately obtained and fine tuned, a camera with a frame speed of about 400 frames per second. These approaches enabled the accurate determination of the incoming and return velocities of the ball, the precise location of the ball’s impact on the strung surface, the dwell time of the ball on the racquet, and the angle of the ball’s return.

Film frames were analyzed, one by one, to determine the ball’s return velocity. The coefficients of restitution (the return velocity divided by the incoming velocity) of points approximately one inch apart were then plotted.

Hence, if the incoming velocity was sixty miles per hour (set by the ball throwing machine) and the return velocity was thirty miles per hour (determined by an analysis of the photograph frames), then the coefficient of restitution was 30/60 or 0.5. The higher the coefficient of restitution, the more power achieved by the racquet. The dwell time of the ball on the strung surface and the angle of return were further measures of the amount of control over the ball by the racquet.

Research Results
Although the Prince racquet’s strung surface was only sixty percent larger than conventional racquets, Head determined that at a widely encountered ball velocity, the average size of the corresponding zones for the Prince racquet was 3.78 times that of the conventional racquet. Likewise, Head sought quantitative parameters to measure the control over ball return. Prior to Head’s work, ball control had been anecdotal. With characteristic impatience, Head determined that this would never do. Instead, he determined that he could quantitatively measure ball control by determining the angle of return, namely the included angle between the incoming trajectory and the outgoing trajectory, and the dwell time of the ball on the racquet’s strings. Head determined that a ball struck off the center of the strung area tends to be returned at an angle materially differing from its incoming trajectory. Head’s tests pointed to the advantages of increasing the strung surface area to control this. To measure the angle of return, Head developed elaborate plots showing the zones where the error in the angle of return was less than 20 degrees and less than 10 degrees.